1. Technical Field
The present disclosure relates to a light emitting device.
2. Description of the Related Art
A semiconductor light emitting diode (LED), having advantages as a light source in terms of output, efficiency, and reliability, has been actively researched and developed as a high output, high efficiency light source that may replace a backlight of illumination devices or display devices.
In general, an LED is driven at a relatively low DC current. Thus, in order to drive an LED with a normal voltage mode (e.g., AC 220V), an additional circuit (e.g., an AC/DC converter) supplying a low DC output voltage is required. However, the introduction of an additional circuit makes a configuration of an LED module complicated and degrades efficiency and reliability due to a process of converting supplied power. In addition, product unit costs are increased due to the additional components besides a light source, the size of a product is increased, and EMI characteristics are degraded due to a periodic component related to a switching mode operation.
In an effort to solve the problems, various types of LED driving circuits have been proposed that may be driven even at an AC voltage without an additional converter. However, an LED has diode characteristics, so it is difficult for only a single LED to be driven with bi-directional AC. Thus, the single LED may be protected by a Zener diode, which is, however, ineffective in size, capacity, and cost in terms of a system, and flicker characteristics may be degraded in uni-directional 60 Hz driving to cause a problem with light quality. In addition, when high voltage AC power is used, a single LED having a driving voltage Vf of about 3˜4V has limitations in effective driving. Thus, in order to make an AC driving LED, a high voltage LED operable bi-directionally at 120 Hz and having a high driving voltage Vf is required.